LG Heat Pump Error Code P751

P751 indicates that the outdoor unit Electronic Expansion Valve (EEV) failed its open position self-diagnosis check. The system commands the EEV to move to the fully open position and verifies the response. When the valve does not perform as expected, the P751 fault is logged and the unit stops normal operation to protect the refrigerant circuit and compressor.

No, continued operation with an unresponsive EEV is not safe for the system. Without proper refrigerant metering, the compressor is at risk of liquid slugging or running without adequate lubrication, either of which can cause severe internal damage. The unit should remain off until the fault is diagnosed and repaired.

A power reset may temporarily clear the fault code, but if the underlying problem with the EEV, its wiring, or the control board is not corrected, the P751 error will return once the system runs its self-diagnostic routine again. Resetting without repair is not a solution and delays proper diagnosis, potentially allowing further damage to the system.

Some causes, such as a loose or damaged wiring harness connector at the EEV, can be addressed by a knowledgeable DIYer with basic electrical tools. However, replacing the EEV valve assembly or the outdoor control board involves working within the refrigerant circuit and with high-voltage components, which requires a certified HVAC technician. Attempting refrigerant-side repairs without proper certification and equipment is unsafe and may be illegal.

Repair costs vary depending on the root cause. A wiring harness repair may cost between $100 and $250 in labor. Replacing the EEV assembly typically ranges from $250 to $600 including parts and labor. Outdoor PCB replacement can range from $400 to $900 or more depending on the model and part availability. Obtaining a diagnostic service call from a licensed technician is the first step to getting an accurate estimate.